The use of photosynthetic algae to produce biofuels is an active area of research and development. Many projects are underway to improve the capability of photosynthetic algae to manufacture metabolites that are useful as sources of energy. In order to provide metabolites useful as biofuels, the algae must be encouraged to fix inorganic carbon into organic molecules, especially dissolved organic metabolites, that can be directed by the metabolic pathways of the algae into compounds useful as biofuels. Manipulation of the metabolic pathways of algae to divert the dissolved organic metabolites into compounds useful as biofuels may be achieved by standard genetic engineering techniques.
Further, in nature, microbial processes are coupled whereby photosynthetic primary producers of fixed carbon release carbon and nitrogen based dissolved organic matter that is assimilated and remineralized by heterotrophic bacteria and archaea. Azam, F., et al., Nat. Rev. Micro. (2007) 5:966, Azam, F., Science (1998) 280:694-696. In some case, biopolymers are released by virtue of apoptosis of the photosynthetic organism. Berges, J. A., et al., Limnol. Oceanogr. (1998) 43:129-135, Bidle, K. D., et al., Eukaryot. Cell (2008) 7:223-236.
The photosynthetic alga Dunaliella salina is the primary photosynthetic organism operative in halophilic environments wherein in such environments D. salina employ CO2 assimilation to produce and store glycerol for use as an osmoprotectant at intracellular concentrations as high as 7M. Liska, A. J., et al., Plant Physiol. (2004) 136:2806-2817. It has also been shown that when exposed to darkness, this alga releases metabolites due to apoptosis as the release can be blocked by caspase inhibitors. Segovia, M., et al., Plant Physiol. (2003) 132:99-105.